Blasting agent



Sept. 11, 1962 Filed June 11, 1957 c. o. DAVIS ET AL 3,053,707

BLASTING AGENT 2 Sheets-Sheet 1 Big INVENTORS CLYDE O. DAVIS JESSE E.HUGHES ATTORNEY Sept. 11, 1962 c. o. DAVIS ETAL BLASTING AGENT 2Sheets-Sheet 2 Filed June 11, 1957 INVENTORS C LY D E O. DAVIS JESSE E.HUGHES ATTORNEY United fitates Fatent 3,053,707 BLASTING AGENT Clyde 0.Davis, Wenonah, and Jesse E. Hughes, Bridgeport, N.J., assignors to E.I. du Pont de Nemours and Company, Wilmington, Del., a corporation ofDelaware Filed June 11, 1957, Ser. No. 665,054 4 Claims. (Cl. 149-8) Thepresent invention relates to a novel blasting agent and to a method forthe preparation of such agent.

In large scale blasting operations, the use of blasting agents free fromhigh explosive ingredients has gained Wide acceptance because of theirsubstantially lower cost and greater safety during storage and handling.The blasting agents most widely used are those based on ammonium nitrateand a non-explosive fuel, such as carbonaceous materials. Thesecompositions, however, have essentially no water resistance, and, untilrecently, were used exclusively packaged in rigid, water-imperviouscontainers. The containers, usually of metal, represent a substantialproportion of the ingredient cost of the assembled package and sealingthe composition in the container represents an added cost inmanufacture. Of considerable importance also is the fact that rigidcontainers will occupy considerably less than the available volume of aborehole. The great majority of boreholes have very irregular walls dueto varying hardness of the strata through which they are drilled,crevices in the strata, and the normal perambulations of the drill.Since the diameter of the container loaded into the borehole cannot begreater than the diameter of the narrowest portion of the borehole, muchspace within the hole will be unoccupied by the composition in thecontainer.

The use of water-insoluble high explosives, particularly TNT, infree-running form to fill such annular space in a borehole has gainedwide acceptance, despite the relatively high cost of the explosive,because of the considerably higher loading density, and, accordingly, ofavailable energy for blasting thus obtained.

The use of ammonium nitrate-fuel compositions packaged in flexible bagsof polymeric materials is also known. Such bags will permit the enclosedcompositions to substantially fill a borehole, provided the bag materialis sufiiciently thin for adequate expansion of the contents.Unfortunately, however, such bags are easily cut or torn by the roughwalls of the borehole, so that little, if any, Water protection isafforded to the contents after loading. For this reason, the use offlexible bag packaged compositions has been completely restricted toessentially dry boreholes.

The loading of granular or prilled ammonium nitrate in admixture with afuel directly into a borehole has also been practiced to some extent.The mixtures, however, are not satisfactorily free-flowing, and tend tobridge in the hole, thus preventing full loading. Further, the loosemixture will not pack to a density over about 0.8 gram per cubiccentimeter. The likelihood of segregation of fuel from the ammoniumnitrate, particularly if any moisture is present, increases theprobability that only a portion of the energy available will actually beobtained.

Accordingly, an object of the present invention is to provide a blastingagent wherein the foregoing disadvantages are overcome. A further objectis to provide a method for preparing such blasting agent. Additionalobjects will become apparent as this invention is more fully described.

The foregoing objects may be attained when we provide as a blastingagent a plurality of geodes of a blend of ammonium nitrate and sodiumnitrate having a melting point below about 128 C., the interior and thesurface of the said geode containing a carbonaceous fuel liquid ree at atemperature below the melting point of the said blend. The geodes inaccordance with this invention are prepared by introducing the blend ofammonium nitrate and sodium nitrate in molten form dropwise below thesurface of a column of the carbonaceous fuel, the temperature of thefuel being above the melting point of the blend at the portion of thecolumn at which the drops enter and below the melting point of the blendbut above the melting point of the fuel below this portion. The dropletsof blend assume a substantially spherical form while in the portion ofthe fuel column at a temperature above the melting point of the blend.As the drops descend, solidification occurs when the drops are in theportion of the fuel column at a temperature below the melting point ofthe blend. The outer surface of the drop crystallizes first, andcrystallization proceeds inwardly as the heat flows from the drop to thefuel. Because the crystals of sodium nitrate and ammonium nitrate are ofhigher density than the blend in molten form, shrinkage occurs, thusproducing a typical geode. The shell of the geode is sufficiently porousso that the liquid fuel is drawn into the cavity in the center of thegeode. When the geodes thus formed are strained to remove excess liquid,a light coating of the fuel remains on the surface of the geode. Thiscombination of surface coating and core of fuel provides an essentiallyunseparable combination of oxidizing agent and fuel and the sphericalform permits attainments of a relatively high bulk density.

The term geode is widely used in crystallography to describe a more orless spherical shell of crystalline material having a central cavity.The inner surface of a geode may be covered with projecting crystals sothat the cavity is not clearly defined, but represents a portion ofconsiderably less density than the shell. This formation is frequentlyfound in nature with material such as quartz and calcite, and is,therefore, more freuqently associated with mineral aggregates. However,the structure of the ammonium nitrate-sodium nitrate crystals producedby the described method so closely resembles the mineral geodes that theapplication of the term to the present particles is appropriate.

In order to more fully illustrate the method by which the geodes of thepresent invention are prepared, reference is now made to theaccompanying figures. FIG- URE l is an enlarged photograph of a centersection of a geode prepared in accordance with the present invention;FIGURE 2 is an enlarged photograph of a slice through the center of ageode prepared in accordance with this invention, and FIGURE 3 is aschematic drawing of an apparatus for preparing the described geodes.

Referring now to the figures in greater detail, in FIG- URES l and 2 thecavity in the central portion of the spherical mass of crystallinematerial is clearly evident. In the slice shown in FIGURE 2, a fragmentnear the cavity has broken loose from the walls, but the generalconfiguration of the geode is evident. The geodes pictured had an actualdiameter of about 6 millimeters.

In FIGURE 3, 1 represents a melt tank containing a .heating coil 2 and adropping tip 3. The melt tank 1 is mounted over a column 4 which has aheating element 5 about its upper portion. At the bottom of column 4 isa distributor 6 and connected thereto are flow tubes 7 and 8. Tube 8 isconnected to the liquid return tube 8. Flow tube 7 leads to the top of areceiver 9 which contains a strainer element 10 and a fluid dischargetube 11. The tube 11 is connected to the exhaust opening of pump 12. Arepresents molten ammonium nitrate-solium nitrate blend, B representssolidified blend in final form, and C represents liquid fuel.

The operation is as follows: The blend A is melted and maintained inmolten form in melt tank 1 by means of heat from coils 2, which maycontain steam under pressure. The molten blend B flows through droppingtip 3, leaving there in the form of separated drops. The liquid fuel Csurrounding tip 3 is maintained at a temperature higher than the meltingpoint of blend A by means of heating coils 5, so that no solidificationof blend A can occur in either the dropping tip 3 or for a shortinterval after the drop frees itself from tip 3. As the drop descends inthe fuel C in column 4, it reaches a zone where the temperature of fuelC is below the freezing point of the blend A, and solidifies to formgeode B. When geode B enters the distributor 6, the flow of fuel Ccarries it through tube 7 to the receiver 9. The geode B is held on thestrainer 10 while excess fuel C continues on to circulating pump 12 andback to the column 4 through tube 8. This circulation of the fuel C inthe lower portion of column 4 helps maintain a lower temperature in thecooling portion of column 4.

The method of the present invention is further illustrated by thefollowing examples. All parts given are by weight.

EXAMPLE I Using an apparatus arrangement similar to that described inthe drawing, geodes were prepared as follows: a mixture of 80 partsammonium nitrate and 20 parts sodium nitrate was introduced into themelting pot and heated to a temperature of 150 C. In this proportion,the blend formed a eutectic which had a melting point of 120 C., so thatat 150 C. the blend was easily flowable. The molten blend passed througha dropping tip having an internal diameter of 3.175 millimeters into acolumn of kerosene. At the portion of the column surrounding thedropping tip, the temperature of the kerosene was 130 C. and at thebottom of the column about 7 feet from the dropping tip, the temperatureof the kerosene was 40 C.

The pellets produced were spherical and had an outside diameter of from4 to 6 millimeters. When they were broken, the presence of a centralcavity was readily observable. The pellets, after straining, containedabout 4% by weight of kerosene entrapped in the core and on the surfaceof the pellet. The pellets were free-flowing, had a ballistic mortarstrength of 11.1, and a bulk density of about 1.0 gram per cubiccentimeter.

EXAMPLE II In a run identical with that described in Example I, exceptthat dinitrotoluene was used in the column instead of kerosene, pelletsof essentially identical size and form were obtained, but in this casecontained from 4 to 7% by weight of dinitrotoluene in their cores and ontheir surfaces. These pellets were also free-flowing and had a ballisticmortar strength of 9.5. Their bulk density was about 1.0 gram per cubiccentimeter.

EXAMPLE III The procedure of Example I was repeated, except that themixture consisted of 72 parts of ammonium nitrate, 18 parts of sodiumnitrate and 10 parts of urea. The melting point of the trinary eutecticthus formed is about 100 C., therefore the blend was heated to about 135C., and the kerosene in the portion of the column surrounding thedropping tip was heated to about 110 C. The pellets were of essentiallythe same size and form as obtained in Example I, and contained about thesame proportion of kerosene.

EXAMPLE IV A mixture of 66 parts of ammonium nitrate, 14 parts of sodiumnitrate and 20 parts of potassium nitrate (melting point --121 C.) washeated to about 135 C. and fed dropwise through a dropping tip having aninternal diameter of 3.175 millimeters into a column of kerosene. Thetemperature at the top of the column was about 130 C. The geodesobtained had a diameter of from 4 to 6 millimeters and a bulk density of1.03 grams per cubic centimeter. The geodes, when initiated by a primer,detonated at a velocity of 1440 meters per second. The kerosene contentwas between 4 and 5% by weight.

EXAMPLE V A mixture of 50 parts of ammonium nitrate, 33 parts of sodiumnitrate, 10 parts of urea, and 7 parts of potassium nitrate (meltingpoint 57 C.) was heated to C. and fed dropwise through a dropping tubehaving an inner diameter of 3.75 millimeters into a column ofdinitrotoluene at C. at the top and 25 C. at the bottom. The geodesformed had a diameter of about 6 millimeters, a bulk density of 1.02gramsper cubic centimeter, and a DNT content of about 7% by weight. Thegeodes detonated at a velocity of 2310 meters per second.

EXAMPLE VI The procedure of Example III was followed, except thatdinitrotoluene was used in the column and the dropping tip had an innerdiameter at the dropping end of 6.35 millimeters, geodes having anaverage diameter of about 9 millimeters were obtained. The geodes had abulk density of slightly under 1.0 gram per cubic centimeter, adinitrotoluene content of about 6% by weight, and detonated at avelocity of 2000 meters per second. The geodes were shot in a 6-inchdiameter borehole in a quarry and gave excellent blasting action.

Geodes prepared in accordance with the present invention may be coatedwith various materials to increase their water resistance or retardsetting. The geodes may also be coated with combustible materials toincrease the quantity of fuel adhering to the geode. The geodes arefree-flowing and will not bridge when poured into a borehole, providedthey have a diameter of at least 4 millimeters. Smaller particles alsodo not have an internal cavity of suflicient size to hold the desiredamount of fuel within the geode itself. Geodes having a diameter of morethan 12 millimeters are unsatisfactorily fragile. Accordingly, we preferthat the geodes have -a diameter between about 4 and 12 millimeters. Thediameter of the geode is primarily dependent upon the diameter of theopening of the dropping tube, the density of the fuel in the zone inwhich the geode composition is liquid, and the density of the moltengeode composition. To a lesser degree, geode size is also effected bythe viscosity of the fuel, the pressure on the molten composition suchas produced by the depth of the melt, and the configuration of thedropping tip. The temperature of both the melt and the fuel influencestheir density, the flowability of the melt, and the viscosity of thefuel.

We have found that a dropping tip having an opening of smaller diameterthan about 1.4 millimeters will not permit sufliciently rapid flow ofthe melt for satisfactory operation, and the pellets produced areundesirably small with respect to diameter. On the other hand, when thediameter of the dropping tube opening is greater than about 7.0millimeters, the melt has a tendency to fiow as a continuous columnrather than in the form of droplets. Even if droplets are formed, theyare of such large diameter that the geodes formed lack the structuralitrlength to withstand packing and leading into a bore- 1 o e.

Obviously, the density of the fuel used as a coolant for the ammoniumnitrate-sodium nitrate melt must be lower than that of the melt, or thedroplet would not flow downward from the dropping tip. The largestgeodes for a specific dropping tube are obtained when the densities ofthe melt and of the fuel are not very far apart. The following tableshows the effect of fuel density on geode diameter. The melt compositionconsisted of 80 parts of ammonium nitrate and 20 parts of sodiumnitrate, which at a temperature of C. had a density of 1.83 grams percubic centimeter. The

-rtemperature ranges are suitable fuels.

dropping tube had a diameter of 0.318 millimeter. The fuel at thedropping tube was at a temperature of 130 C.

The density of the fuel can obviously be controlled by selection of thefuel, and the density of the melt can be regulated by variation in thecomposition. For example, as previously indicated, an 80/20 ammoniumnitrate/ sodium nitrate melt has a density of 1.83 grams per cubiccentimeter. The density of 72/ 18/ IO-ammonium nitrate/ sodiumnitrate/urea melt is 1.79 grams per cubic centimeter. The density of 72/2-0/ 8-ammonium nitrate/ sodium nitrate/potassium nitrate melt is 1.87grams per cubic centimeter.

A feature of the present invention which is critical is the use of amixture of ammonium nitrate and sodium nitrate which forms a eutectichaving a melting point below 128 C. At temperatures higher than about140 C., the temperature required to maintain a material melting at 128C. in a pourable, fluid state, the operating difliculties increasedrastically and the number of fuels which can be used is greatlyreduced. Further, at temperatures over 140 C., spontaneous reaction ofthe oxidizing agent and the fuel are likely to occur. The fuel obviouslymust be liquid at the temperature at which the ammonium nitrate-sodiumnitrate mixture is fluid and also a temperature at which the mixture issufficiently solidified to permit removal of the geodes from the fuel.

The aliphatic and aromatic hydrocarbons, both substituted andunsubstituted, which are liquid at the desired For reasons of economy,low cost materials such as motor oils, kerosene, dinitrotoluene, and thelike are preferred.

As shown in the examples, the melting point of the ammoniumnitrate-sodium nitrate composition can be lowered by the addition ofmelting point depressants such as urea. The presence of a combustiblemelting point depressant is additionally advantageous in that the fuelcontent of the geode is thereby increased. The inclusion of potassiumnitrate is advantageous because of the stabilizing effect of thepotassium nitrate on the crystal density of ammonium nitrate due totemperature changes. However, both the melting point depressants and thepotassium nitrate represent ingredients whose cost is greater than thatof the basic ingredients needed to produce a blasting agent inaccordance with this invention,

and, in some cases, the additional cost may ofifset the advantagesresulting from their inclusion. Accordingly, this inclusion represents aprefered embodiment rather than a critical feature of this invention.

The geodes produced in accordance with the present invention may be usedin all types of blasting. For example, they may be used to supplementpackaged explosives in a borehole or they may be used as the mainblasting charge. They are particularly advantageous, however, when usedin boreholes which contain standing Water. The term standing water isused to refer to the presence of a collected body of water in a boreholeas distinguished from wet walls and muck in the bottom of the borehole.The geodes of the present invention, because of their high absolutedensity, 1.6 to 1.72 grams per cubic centimeter, sink rapidly to thebottom of the borehole. As geodes on the bottom dissolve, the geodesabove them settle, thus preventing the fuel released from segregating.When the hole is initiated, the blasting energy of all of the oxidizingagent-fuel combination is thus available.

The present invention has been described in detail in the foregoing.Many modifications and variations will occur to those skilled in theart, and we intend, therefore, to be limited only by the followingclaims.

We claim:

1. A blasting agent comprising a plurality of geodes having a diameterbetween 4 and 12 millimeters and consisting essentially of a blend ofammonium nitrate and sodium nitrate having a melting point belo'w 128C., the interior and the surface of said geode containing from 4 to 7%by weight of a carbonaceous fuel selected from the group consisting ofdinitrotoluene, kerosene and castor oil.

2. A blasting agent as claimed in claim 1, wherein urea is incorporatedinto said blend as a melting point depressant.

3. A blasting agent as claimed in claim 1, wherein said carbonaceousfuel is dinitrotoluene.

4. A blasting agent as claimed in claim 1, wherein said blend includespotassium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS1,613,335 Symmes Jan. 4, 1927 2,033,198 Kirst Mar. 10, 1936 2,087,285Handforth et al. July 20, 1937 2,353,147 Cook July 11, 1944 2,398,071Barab Apr. 9, 1946 2,460,375 Whetstone Feb. 1, 1949 2,548,693 Whetstoneet a1 Apr. 10, 1951 2,630,379 Lytle Mar. 3, 1953 FOREIGN PATENTS 152,199Great Britain Oct. 14, 1920

1. A BLASTING AGENT COMPRISING A PLURALITY OF GEODES HAVING A DIAMETERBETWEEN 4 AND 12 MILLIMETERS AND CONSISTING ESSENTIALLY OF A BLEND OFMMONIUM NITRATE AND SODIUM NITRATE HAVING A MELTING POINT BELOW 128* C,THE INTERIOR AND THE SURFACE OF SAID GERODE CONTAINING FROM 4 TO 7% BYWEIGHT OF A CARBONACEOUS FUEL SELECTED FROM THE GROUP CONSISTING OFDINITROTOLUNE, KEROSINE AND CASTOR OIL.